Ok, remember we live in America and we have a right to privacy. Your landlord has crossed the line and even if your lease says he/she can come and go as they please in your apartment, it may be against public policy and the law.
I would send the landlord a very specific letter requesting that he/she cease and desist such activity immediately. It seems clear to me that if the behavior continues you may have the right to void the lease.
Remember you need to keep a paper trial of the offensive behavior. Maybe even a video while you are not home.It sounds like it is time to move on...no pun intended.
Hope the above helps and good luck
